The proposed research is a continuation of ongoing investigations and aims to clarify the mechanism(s) involved in the influence of thyroid hormones in brain development. Particular emphasis will be given to characterize the properties and functional role of specific thyroid hormone receptors in the brain and to identify changes in the density and/or affinity of these receptors in the developing and adult brain. Additional studies examine the involvement of alterations in monoamine metabolism in the functional and behavioral deficits associated with hypo- and hyperthyroidism. BIBLIOGRAPHIC REFERECNES: Valcana, T., Einstein, E.R., Csejtey, J., Dalal, K.B. and Timiras, P.S. Influecne of thyroid hormones on myelin proteins in the developing rat brain. J. Neural. Sci., 25:19-27, 1975. Valcana, T. and Timiras, P.S. Triiodothyronine binding to neuronal nuclei for eu- and hypo-thyroid rats. Trans. Amer. Soc. for Nurochem., 7(1):184, 1976.